Interpretive Summary: Dry cow therapy decreases udder infections of beef cows at the subsequent calving by eliminating infections that exist at drying-off and reducing the incidence of new infections during the dry period. The SCC of quarters infected with mastitis causing bacteria at drying-off was reduced with dry cow therapy, indicating that dry cow treatment improves udder health of beef cow. Administering intramammary antibiotics to beef cows at drying-off can reduce the incidence of udder infections in beef cows after calving and increase weight gain of calves during the subsequent lactation.

Technical Abstract:
Spring calving Angus and Angus x Hereford multiparous cows were utilized to determine the effects of intramammary treatment with penicillin G procain and novobiocin at the time of drying-off on udder health and calf growth following the subsequent calving. Cows were blocked by age and randomly assigned to receive intramammary treatment (n = 99) at drying-off or untreated controls (n = 97). Quarter milk samples were collected at drying-off and at 8-14 d after calving. Milk samples were analyzed for somatic cell counts (SCC) and mastitis causing bacteria. Dry cow treatment decreased (P < 0.01) the number of cows and quarters infected after calving. Treatment decreased (P < 0.05) the number of cows that developed new infections and reduced (P < 0.05) quarters with the number of mastitis causing bacteria that were infected at weaning: SCC after calving were greater for cows infected with mastitis causing bacteria. Treatment did not alter (P > 0.1) SCC of quarters after calving that were infected with Staphylococcus aureus at drying-off, but reduced (P < 0.05) SCC after calving of quarters that were infected with coagulase-negative staphylococci at drying-off. Weight of calves during early lactation was increased (P = 0.03) in cows with intramammary infection and treated at drying-off. Treatment of non-infected cows at drying-off, increased (P = 0.008) adjusted 205 d weaning weights of calves after the subsequent lactation when compared to untreated non-infected cows. We conclude that treatment of beef cows at drying-off with intramammary antibiotics decreased intramammary infections after calving, improved udder health during the subsequent lactation, and increased weight gain of calves.